THE BENEFITS OF USING TREES FOR NATURAL STORMWATER MANAGEMENT

Natural stormwater management is an approach that utilizes natural systems to control and mitigate the effects of stormwater runoff. One highly effective and sustainable element of this approach is the use of trees. Trees offer numerous benefits for stormwater management, including reducing runoff, preventing erosion, improving water quality, and enhancing overall environmental resilience. This note explores these benefits in detail, highlighting the critical role that trees play in natural stormwater management.

Reduction of Runoff: Trees play a vital role in reducing stormwater runoff by intercepting and absorbing rainfall. Their canopies act as natural umbrellas, capturing raindrops and allowing them to evaporate or drip slowly to the ground. This reduces the volume and velocity of runoff, mitigating the risk of flooding and erosion.
Soil Stabilization and Erosion Prevention: The extensive root systems of trees help stabilize soil and prevent erosion. During heavy rain, tree roots hold the soil in place, reducing the likelihood of landslides or slope failure. The roots also create channels that facilitate water infiltration into the ground, allowing the soil to act as a natural sponge and retain stormwater.
Water Quality Improvement: Trees contribute to improved water quality by filtering stormwater runoff. As water percolates through the soil, tree roots and the associated soil microorganisms act as natural filters, removing pollutants such as sediments, nutrients, heavy metals, and chemicals. This filtration process helps protect water bodies, such as rivers, lakes, and groundwater, from contamination.
Temperature Regulation: Trees can help mitigate the urban heat island effect, which is the phenomenon of increased temperatures in urban areas due to the abundance of impervious surfaces. By providing shade and transpiring water through their leaves, trees cool the surrounding environment. This cooling effect can reduce the volume of stormwater runoff generated and alleviate strain on stormwater infrastructure during intense rainfall events.
Carbon Sequestration and Air Quality Enhancement: Trees are excellent carbon sinks, absorbing carbon dioxide (CO2) from the atmosphere and storing it in their trunks, branches, leaves, and roots. By sequestering carbon, trees help combat climate change and reduce the concentration of greenhouse gases. Additionally, trees improve air quality by absorbing air pollutants and releasing oxygen through photosynthesis, contributing to a healthier and more pleasant urban environment.
Biodiversity and Habitat Creation: Trees support biodiversity by providing habitats for various species, including birds, insects, and small mammals. Urban areas with a rich tree canopy can harbor diverse ecosystems, creating interconnected habitats and promoting wildlife movement. This ecological diversity contributes to the overall resilience of the urban ecosystem and enhances the aesthetic appeal of green spaces.

The benefits of using trees for natural stormwater management are multifaceted and far-reaching. From reducing runoff and preventing erosion to improving water quality, temperature regulation, and carbon sequestration, trees play a vital role in creating sustainable and resilient urban environments. Incorporating trees into stormwater management strategies can help cities and communities combat the adverse effects of stormwater runoff while simultaneously promoting environmental health, biodiversity, and a higher quality of life. Emphasizing the importance of trees in stormwater management is essential for sustainable urban planning and the well-being of both humans and the natural world.

Preserving natural tree canopy and the prudent use of tree plantings in urban landscapes contributes to the control of runoff through a number of mechanisms.

Trees intercept and store runoff and transfer water back to the atmosphere through evapotranspiration, reducing the volume of runoff;
the shade and tree litter beneath the canopy help promote infiltration of precipitation that reaches the ground beneath the tree, providing moisture to the tree roots (ultimately to become transpiration) and reducing the volume of runoff;
roots, tree litter, and vegetative groundcover beneath the trees can slow the travel of runoff, resulting in lower times of concentration than associated with bare earth or impervious surfaces, and thus lowering peak runoff rates;
tree roots, leaf litter, and vegetative cover stabilize the soil surface, preventing erosion and associated impacts; and
trees, associated ground litter, and groundcover provide filtration and vegetative uptake of contaminants, enhancing water quality.

These functions for control of runoff and its impacts are further discussed below.

Interception and Evapotranspiration

Through the processes of interception, evaporation, and transpiration, trees and other vegetation capture and store a portion of rainfall and release water to the atmosphere, reducing the net amount of rainfall that becomes runoff. Rain is captured (intercepted) on a plant’s leaves and stems (for trees, the leaf and stem complex is referred to as “canopy”). A portion of this captured water evaporates back into the atmosphere before reaching the ground. Larger canopies intercept greater amounts of precipitation because there is more surface area available for water molecules to adhere to.

Some water flows down the plant stem to the ground as “stemflow”, and some rainfall infiltrates the ground around the plant, entering the root zone where the plant withdraws moisture to sustain itself. In this process, water taken up through its roots is then released through the plant’s vegetative structures as water vapor, a process known as transpiration. The combination of these two mechanisms – evaporation and transpiration – whereby a plant transfers moisture to the atmosphere is referred to as evapotranspiration. In both processes the water is diverted before ever becoming runoff.

Mature tree canopies are of particular value in the interception of rainfall. For example, in a New Hampshire hardwood forest at the Hubbard Brook LTER site, deciduous trees were observed to intercept 13% of the total rainfall during the leaf period and 12% of the total rainfall during the leafless period (Leonard, 1961).

Individual mature trees also provide significant rainfall interception. An illustration of this potential stormwater benefit using the National Tree Benefit Calculator was cited in Chapter 1 of this report (i.e., greater than 9% annual rainfall capture over the “footprint” of the tree). The significant volumes of interception shown in that example and in the Hubbard Brook study cited above are consistent with findings of other studies throughout the United States.

The amount of rainfall intercepted by vegetation varies depending on the type of species, time of year, and intensity and duration of the rainfall event. Species characteristics like leaf surface area and specific tree architecture contribute to the variation in total water intercepted. Also, trees typically intercept more rain during a storm of longer duration than a short storm with equal total rainfall accumulation (CUFR, 2002). In areas where rainfall is highest in the fall, winter, and spring, broadleaf evergreens and conifers intercept more rainfall than deciduous species (Xiao and McPherson 2002).

Promotion of Infiltration

Another crucial role plants have in reducing landscape runoff is facilitating ground water infiltration. Plants provide suitable conditions for water to infiltrate through several mechanisms. Decomposing plant material on the ground captures and temporarily stores runoff. Root systems create large pores in the soil called macropores that facilitate infiltration. Tree roots provide pathways for stormwater infiltration to enter soils compacted by development activity (e.g., see Bartens, et.al., 2008). The uptake of water from the soil by plants between rainfall events frees pore space that then becomes available for storage during a subsequent storm.

Note, however, that in the case of trees, much of the infiltrated water will ultimately be taken up by the trees themselves, so that in areas with extensive tree cover, deep groundwater recharge may actually be less than in areas with little or no tree cover.

Vegetative Retardance of Runoff

Vegetation not only reduces the volume of runoff, but can also reduce runoff velocity compared to flow over an un-vegetated surface (an effect referred to as vegetative retardance). This results in longer times of concentration. Natural surface roughness associated with vegetation contributes to lower peak rates of discharge than would occur on an un-vegetated landscape. Maintaining and restoring vegetated landscapes thus can contribute to the control of the rate runoff is transported through a drainage basin.

Surface Stabilization

Trees and other vegetation throughout the landscape stabilize slopes and channels and prevent soil erosion. Trees protect soil from direct exposure to falling rain by intercepting rain, absorbing the impact of rainfall that does drip from the leaf surface to the ground, and providing leaf litter that absorbs the impact of rainfall as it hits the ground. Each of these mechanisms helps prevent dislodgement of soil particles by rainfall. Additionally, the tree’s root system keeps soils intact, stabilizing slopes against displacement by runoff flowing over and through the surface soils. Reduced erosion rates from vegetated landscapes protect the quality of receiving waters by minimizing transport of sediments and associated pollutants.

Water Quality Enhancement

Not only can trees reduce the total amount and rate of stormwater runoff, they can also improve the water quality of runoff. The forest litter associated with woody plants (as well as groundcovers that may thrive beneath trees) can filter runoff as it passes over the ground. Woody plants in particular can uptake nutrients, contaminants, and metals from water or soil. A study showed that within one growing season a maple removed 60 mg of cadmium, 140 mg of chromium, 820 mg of nickel, and 5200 mg of lead (Coder, 1996). Vegetative pollutant uptake improves the surrounding soil and water quality, resulting in less contamination in runoff reaching the stormwater system from tree covered landscapes and from stormwater treatment practices that include tree plantings.

An additional water quality benefit provided by tree canopy comprises moderation of the thermal impacts of stormwater runoff. For discharges to temperature-sensitive water resources such as coldwater fisheries, prudent preservation or enhancement of tree cover to shade impervious surfaces (where runoff originates), outlet channels (where runoff discharges), and stream banks can moderate temperatures of stormwater discharges.

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The Year-Round Importance of Tree Service: Nurturing Tree Health and Enhancing Property Care

Introduction:

Trees are not only beautiful additions to our landscapes but also vital contributors to the health of our environment. Proper tree care and maintenance are essential year-round to ensure the well-being of trees and their surrounding properties. In this comprehensive article, we explore the numerous reasons why tree service is important throughout the year, using keywords such as trees, tree care, tree maintenance, tree services, pruning, tree removal, and more. By understanding the significance of professional tree care, we can enhance tree health, protect our properties, and foster a sustainable environment.

Promoting Tree Health:

Tree service plays a fundamental role in promoting the health and vitality of trees. Regular tree care, such as pruning, trimming, and proper watering, helps maintain strong, well-shaped trees. By removing dead or diseased branches, arborists ensure that trees can allocate their resources towards healthy growth, preventing the spread of diseases and pests.

Enhancing Property Care:

Trees contribute significantly to the aesthetics and value of a property. Professional tree service enhances the overall care and appearance of your home or business premises. Through tree trimming, pruning, and removal of hazardous limbs, arborists maintain a well-manicured landscape, ensuring that trees complement the property’s architectural features and create an inviting curb appeal.

Preventing Property Damage:

Unkempt or unhealthy trees can pose a risk to both your property and personal safety. During storms or high winds, weak branches or overgrown trees can fall, causing damage to structures, vehicles, or power lines. Regular tree service minimizes these risks by identifying and addressing weak or dangerous limbs, reducing the likelihood of property damage and potential injuries.

Ensuring Safety:

Professional tree service guarantees safety not only for property owners but also for the arborists themselves. Tree care specialists possess the necessary skills, equipment, and knowledge to handle challenging tree maintenance tasks, such as working at heights or near power lines. Their expertise ensures a safe and efficient job while mitigating risks associated with tree care.

Tree Maintenance Throughout the Year:

Different seasons present varying challenges and opportunities for tree care. During the winter months, tree service focuses on pruning and removing dead branches, which can prevent damage caused by heavy snow or ice. In the spring, arborists engage in trimming and pruning to encourage healthy growth and shape trees. Summer tree care includes adequate watering and pest control measures, while autumn calls for leaf removal and preparation for colder months.

Environmental Benefits:

Trees play a crucial role in mitigating climate change by absorbing carbon dioxide, reducing air pollution, and providing shade, which helps regulate temperatures. Tree service, including proper planting, mulching, and care, ensures that trees thrive and continue to contribute to a healthier environment, combatting global warming and promoting cleaner air and stormwater runoff management.

Preserving Tree Species and Biodiversity:

Professional tree service extends beyond individual tree care; it encompasses the preservation of diverse tree species. Arborists understand the unique needs of different types of trees, such as evergreens, deciduous, coniferous, or palm trees. By providing appropriate care, including disease prevention, soil management, and maintenance, tree service professionals contribute to the preservation of a rich tree population and overall biodiversity.

Expertise and Equipment:

Tree service companies employ trained and certified arborists who possess in-depth knowledge of tree biology, growth patterns, and proper care techniques. These professionals are equipped with specialized tools and equipment necessary for tasks like tree removal, stump grinding, or emergency storm response. Their expertise and tools ensure that tree care is conducted efficiently and with minimal disruption to the property.

Long-Term Cost Savings:

Investing in professional tree service may seem like an additional expense, but it often translates into long-term cost savings. Regular tree maintenance, including pruning, prevents the need for extensive tree removal or expensive repairs caused by fallen limbs or property damage. Proactive care can also prevent diseases or pests from spreading, saving property owners from costly treatments or tree replacements.

Conservation and Sustainability:

Tree service aligns with the principles of conservation and sustainability. Arborists prioritize preserving healthy trees whenever possible and resort to removal only when necessary. Furthermore, they provide guidance on tree planting, helping property owners select appropriate species for their specific areas, considering factors like climate, soil conditions, and available space.

Conclusion:

Tree service is a year-round commitment to nurturing tree health, protecting properties, and fostering a sustainable environment. By investing in professional tree care, property owners ensure the long-term vitality and beauty of their trees, enhance property value, and contribute to a healthier planet. Embracing the expertise of arborists and understanding the importance of proper tree maintenance, we can enjoy the numerous benefits that trees provide while preserving their beauty for generations to come.